Semiconductor device

ABSTRACT

A method for fabricating a semiconductor device includes the formation of a monitoring element in a substrate. The monitoring element has substantially the same structure and size as a circuit element on the device which is to be monitored. Polycrystalline electrodes are contacted to the semiconductor regions of the monitoring element and extend on an insulating film covering the surface of the substrate. The electrical characteristics of the monitoring element are measured by contacting probes of a measuring apparatus to portions of the polycrystalline electrodes.

This is a continuation of Ser. No. 746,744, filed Dec. 2, 1976, nowabandoned.

This invention relates generally to semiconductor devices, andparticularly to a semiconductor integrated circuit device having asemiconductor element for monitoring characteristics of the device.

In a semiconductor integrated circuit device, one or more auxiliarysemiconductor elements are provided for the purpose of monitoring ormeasuring characteristics of the semiconductor elements included in thedevice. The size and structure of such auxiliary element should bepreferably the same as those of the element to be monitored. However,recently developed semiconductor elements of highly reduced size make itimpossible to contact the probes of a measuring apparatus directly ontothe surface of the element. Therefore, monitoring of the characteristicsof elements in an integrated circuit device has been recently done byway of either (1) using external lead-out electrodes furnished to thesame-sized auxiliary element or (2) resorting to a large-sized auxiliaryelement whose characteristics are correlated with those of a small-sizedelement to be monitored. In the latter method (2) the characteristics ofthe element to be monitored must be calculated and estimated from thosemeasured of the large-sized auxiliary element and therefore this methodis complicated and inaccurate. The former method (1) can readilydetermine the characteristics of the element with accuracy but thecharacteristics of the element cannot be modified to their desiredvalues, because the aluminum that is commonly employed for the externallead-out electrodes cannot stand the treatments that are necessary formodifying the characteristics of the element.

A polycrystalline silicon layer is widely used in a semiconductorintegrated circuit device, for example, as a gate electrode of aninsulated-gate field-effect transistor, as an impurify source fordiffusion and an electrode of the diffused region in a bipolartransistor, or as a thin film resistor. The characteristics of suchsemiconductor devices using a polycrystalline silicon layer, however,cannot be ascertained until the metallic electrodes for externallead-out are formed, and at that stage, modification of thecharacteristics is impossible.

An object of this invention is, therefore, to provide a semiconductordevice in which the characteristics of an element involved therein canbe readily monitored and modified.

Another object of this invention is to provide a semiconductorintegrated circuit device including a semiconductor element withexternal lead-out electrodes for monitoring, which can be subjected totreatment to modify its characteristics.

A further object of this invention is to provide a method ofmanufacturing a semiconductor device, in which the characteristics of anelement involved in the device can be determined through a monitoringelement and subsequently modified to desired values.

This invention is featured by the use of a polycrystalline silicon layerfor the external lead-out electrodes to be used for monitoring thecharacteristics of a semiconductor element included in a semiconductorintegrated circuit device. The silicon external lead-out electrodes areconnected to a monitoring semiconductor element, which is, in turn,formed in, or on, the same semiconductor substrate as the semiconductorintegrated circuit device, and extended on an insulating film coveringthe semiconductor substrate to an area outside the area of themonitoring semiconductor element. The monitoring semiconductor elementmay be provided auxiliarily in addition to the elements constituting theintegrated circuit, or it may be one constituting the integrated circuitdevice. The size and the structure of the monitoring semiconductorelement are preferably the same as those of a semiconducor element to bemonitored. According to this invention, probes of a measuring apparatusare contacted to the silicon external lead-out electrodes to measure thecharacteristics of the monitoring element and thereby to determine thecharacteristics of the element to be monitored. If the measuredcharacteristics are not at their desired values, the device is subjectedto an extra treatment of, for example, heat treatment or impurityaddition to bring the characteristics to the desired values. Thecharacteristics are again checked by contacting the probes to thesilicon electrodes of the monitoring element. Thereafter, once themonitored characteristics are of the desired values, metallic electrodesor metallic wiring layers, if used, are formed on the device. With themonitoring terminal electrodes of silicon which can stand the hightemperature of the characteristics-modifying treatment, both themonitoring and modifying of the characteristics can be carried outreadily and accurately. Moreover, metallic electrodes or wiring layerscan be used while carrying out both the monitoring and modifyingprocesses.

Other features and objects of this invention will become more apparentfrom the following description of preferred embodiments of theinvention, taking in conjunction with the accompanying drawings inwhich:

FIGS. 1A to 1G are cross sections of a monitoring bipolar transistoraccording to an embodiment of this invention in respective steps ofmanufacture; FIG. 1H is a plan view of the transistor, FIG. 1G is across sectional view taken along the line X-X' of FIG. 1H;

FIGS. 2A to 2F are cross sections of a monitoring resistor according toanother embodiment of this invention in respective steps of manufacture;FIG. 2G is a plan view thereof and, FIG. 2F is a cross-sectional viewtaken along the line Y-Y' of FIG. 2G;

FIG. 3A is a cross sectional view along the line Z-Z' of FIG. 3B showinga part of an integrated circuit device including a monitoring transistoraccording to this invention; FIG. 3B is a plan view thereof;

FIG. 4 is a cross-sectional view of another monitoring transistoraccording to this invention; and

FIG. 5 is a cross sectional view of another monitoring resistoraccording to this invention.

In a first embodiment of this invention shown in FIG. 1, the surface ofan N-type silicon substrate 2 is thermally oxidized and thereby coveredwith a silicon oxide film 1 (FIG. 1A). Then, an opening (not shown) isformed in the silicon oxide film 1 to partially expose the surface ofthe substrate 2 and boron atoms are diffused through that opening intothe N-type silicon substrate to form a P-type base region 3 there, thesurface thereof being covered with a silicon oxide film 1 (FIG. 1B).Then, openings 4, 5 and 6 are formed in the silicon oxide film 1 (FIG.1C). The openings 4, 5 and 6 are used to enable ohmic connectionsbetween silicon lead-out electrodes and the base, emitter and collectorregions of a monitoring transistor, respectively, in subsequent steps.

A layer of polycrystalline silicon 7 is then deposited by thermaldecomposition of monosilane over the substrate surface, that is, on thesilicon oxide film 1 and in the openings 4, 5, and 6 (FIG. 1D). Thepolycrystalline silicon layer 7 is then selectively removed to formpolycrystalline silicon external lead-out electrodes 8, 9 and 10 for thebase, emmiter, and collector, respectively and the surfaces of therespective silicon electrodes 8, 9 and 10 are covered with a siliconoxide film by thermal oxidation (FIG. 1E). Referring also to FIG. 1H,the silicon electrodes, 8, 9 and 10 are connected respectively to thebase region 3, the prospective emitter region, and the collector region2 and extend on the surface of the silicon oxide film 1. Each of thesilicon electrodes 8, 9 and 10 extends on the oxide film 1 to an areaoutside the active area of a monitoring transistor element and thereterminates in a pad portion 8', 9', 10' of a wide area adapted toreceive a probe of a measuring apparatus. The area of the pad portionand the distance of the adjacent pad portions are determined to ensurethat one probe of a measuring apparatus contacts exclusively a singlepad portion.

The oxide film covering the base lead-out electrode 8 is then removedand boron atoms are diffused through the base electrode 8 ofpolycrystalline silicon via the base opening 4 into the P-type baseregion 3 to form a P⁺ -type base contact region 3' therein, the surfaceof the base electrode 8 being again covered with an oxide film bythermal oxidation (FIG. 1F). The oxide films covering the emitter andcollector lead-out electrodes 9 and 10 are then removed, and phosphorusatoms are diffused through the emitter and collector electrodes 9 and 10via the emitter and collector openings 5 and 6 into the base region 3and the collector region 2, respectively, to form an N-type emitterregion 11 in the base region 3 and an N⁺ -type collector contact region(FIG. 1G).

The silicon electrodes 8 and 10 are sufficiently doped with an N-typeimpurity, e.g. phosphrous and covered with an oxide film. The oxidefilms covering the silicon lead-out electrodes 8 to 10 are removed atleast from the surface of the respective pad portions 8' to 10', and bycontacting probes of a measuring apparatus to the exposed pad portions8' to 10' of the silicon lead-out electrodes 8 to 10 as the monitoringterminals, characteristics of this monitoring transistor, such as itsemitter-grounded current gain h_(FE), are measured. If the measuredcharacteristics are lower than the desired values, further diffusion ofimpurity or impurities is performed. For instance, when phosphorus wasdiffused at a temperature of 1000° C. for 25 minutes through the emitterand collector electrodes 9 and 10 of the silicon layer of approximately0.5 μm thick to form an emitter region 11 having a spare area of 4=4 μmwith a distance of 0.8 μm from the collector region 1, the current gainh_(FE) measured was 20. Since this value was lower than the desired one,the device was heated at a temperature of 1000° C. for 30 minutes in anitrogen atmosphere to diffuse phosphorus doped in the emitter electrode9 into the emitter region 11. As a result of measurement by use of thesilicon lead-out electrodes 8, 9 and 10 the current gain h_(FE) wasincreased to 60. Under such high temperature treatment, alumimumelectrodes would have been melted out.

In a second embodiment of the invention shown in FIG. 2, a semiconductorsubstrate 2 is thermally oxidized to form an oxide film 1 (FIG. 2A). Apolycrystalline silicon layer 7 is then deposited on the oxide film 1 bythermal decomposition of monosilane and is selectively removed to form aresistor element with terminal portions (FIG. 2B). Referring to FIG. 2G,the terminal portions 12 and 13 connect to both ends of the body 14 ofthe resistor element and extend on the oxide film 1 to pad portions 12'and 13' having a wide area which serve as monitoring terminalelectrodes. The whole surface of the silicon resistor element is coveredwith an oxide film by thermal oxidation.

The oxide film covering the silicon resistor element is then selectivelyremoved from both end terminal portions 12 and 13 (including padportions 12' and 13') of the silicon resistor element (FIG. 2C), andboron is diffused in to the exposed end terminal portions 12 and 13 toconvert them into highly-doped low-resistance regions (FIG. 2D). The endterminal portions are again covered with an oxide film. Then, the body14 of the silicon resistor element is exposed (FIG. 2E) and doped withboron atoms of a controlled amount by ion implantation to gain a desiredresistivity value and is again covered with a silicon oxide film (FIG.2F).

The pad portions 12' and 13' of the terminal of the resistor element areexposed and probes of a testing apparatus are put into contact theretoto measure the resistivity of the monitoring resist element. If theresistivity is found to be lower than a desired value, the thickness ofthe silicon layer at the body 14 of the monitoring and of anotherresistor to be monitored which has been formed on the same oxide film 1at the same time and by the same process as the fabrication of themonitoring resistor is reduced to enhance the resistivity. If themeasured value of resistance is higher than the desired value,impurities are further introduced into the body 14 of the resistors toreduce the resistivity.

FIG. 3 shows a part of a semiconductor integrated circuit device inwhich a monitoring bipolar transistor 31 is incorporated together withsemiconductor circuit elements, such as a bipolar transistor 32 and adiffused resistor 33, of the integrated circuit. These circuit elementsare formed in a single semiconductor substrate 42 and are isolated fromeach other by P-N junctions. In detail, a plurality of N-type islandregions 21, 22, 23 are formed in the P-type silicon substrate 42. In oneisland 21, the monitoring transistor 31 having the same structure asthat of the embodiment of FIG. 1 is formed in the same manner as theembodiment of FIG. 1, with its base lead-out electrode 24, emitterlead-out electrode 25 and collector lead-out electrode 26 all formed ofpolycrystalline silicon. In another island 22, the bipolar transistor 32of the same type as the monitoring transistor 31 is formed with itssilicon collector electrode 27, its silicon emitter electrode 28extending to another element and its silicon base electrode 29 extendingon an oxide film 41 covering the substrate 42 to and connected to oneterminal of the diffused resistor 33. An aluminum wiring layer 43 isconnected to the silicon collector electrode 27 and extends to anotherelement. The other terminal of the resistor 33 is connected to anotherelement through a silicon electrode 30 and an aluminum wiring layer 44.The P-type base region 51 of the monitor transistor 31, the P-type baseregin 52 of the circuit transistor 32, and the P type resistor region 53are formed at the same time in the N-type islands 21, 22, and 23,respectively. Then, the silicon electrodes 24 to 30 are formed at thesame time. P⁺ -type base contact regions 54 and 55 and P⁺ -type resistorcontact regions 56 are then formed also at the same time and N⁺ -typeemitter regions 57 and 58 and N⁺ -type collector contact regions 59 and60 are all formed simultaneously. Thereafter, the characteristics of themonitoring transistor 31 are measured by the use of the monitoringterminals 24, 25 and 26 formed of silicon to monitor the characteristicsof the circuit transistor 32, and, if necessary, the characteristics ofthe transistors 31 and 32 are modified at the same time. Then, thealuminum wiring layers 43 and 44 are formed on the substrate 42. Sincethe transistor 32 used in the integrated circuit is of the same type as,and is formed at the same time as, the monitoring transistor 31, itscharacteristics can be monitored through the monitoring transistor 31and controlled accurately. Moreover, the use of the silicon lead-outelectrodes 24, 25 and 26 as monitoring terminals makes it possible tomodify and control the characteristics of the transistors 31 and 32accurately in the course of manufacture.

Referring to FIGS. 4 and 5, which are respective modifications of theembodiments of FIGS. 1 and 2, polycrystalline silicon lead-outelectrodes 15, 16 and 17 of a monitoring transistor (and of a circuittransistor to be monitored) and end terminal portions 20 and 20' and abody portion 19 of silicon of a monitoring resistor (and of a resistorto be monitored) are embedded in a silicon oxide layer 18 which isformed by the selective oxidation of a silicon layer rather than by theselective removal thereof. This structure makes the surface of thedevice flat.

The monitoring transistor and the monitoring resistor of the inventionmay be used as circuit elements constituting an integrated circuit. Insuch case, the silicon lead-out electrodes 8, 9 and 10, 12, 13 15, 16and 17, 22, 20', and 24, 25 and 26 are connected to other elements byway of, e.g., aluminum wiring layers. Where these silicon lead-outelectrodes are solely used for characteristics-monitoring, they may beretained as they are after monitoring they may be removed by etching orconverted into oxide after monitoring.

I claim:
 1. A method of manufacturing a semiconductor device, comprisingthe steps of forming a plurality of transistor elements and a monitoringtransistor element in a semiconductor substrate, said monitoringtransistor having substantially the same structure and size of atransistor element to be monitored, forming polycrystalline siliconelectrodes connected to the base, emitter, and collector regions of saidmonitoring transistor element and extending on an insulating filmcovering the surface of said semiconductor substrate, measuring thecurrent gain of the monitoring transistor by the use of portions of saidsilicon electrodes extending on said insulating film, modifying thecurrent gain of the transistor elements in said semiconductor substrateto a desired value after said current-gain measuring step, andthereafter forming a metallic layer on an insulating film covering thesurface of said semiconductor substrate after said current-gainmodifying step, said modifying step including the step of heating saidsemiconductor substrate at a temperature above that which said metalliclayer is able to withstand, but which can be withstood by saidpolycrystalline silicon electrode.
 2. A method of manufacturing asemiconductor device comprising the steps of forming a plurality ofcircuit elements and at least one monitoring circuit element in asemiconductor substrate, said monitoring circuit element havingsubstantially the same structure and size as a circuit element to bemonitored, forming electrodes made of polycrystalline silicon for saidmonitoring circuit element to contact with semiconductor regions of saidmonitoring element and extend on an insulating film selectively coveringthe surface of said substrate, the silicon electrodes of said monitoringcircuit element having portions on said insulating film remote from theactive regions of said monitoring circuit element and connected to noother of said circuit elements, measuring the electrical characteristicsof said monitoring circuit elements for detecting directly theelectrical characteristics of said circuit element to be monitored bycontacting probes of a measuring apparatus to said portions of saidsilicon electrodes, modifying the characteristics of said monitoringcircuit element, and thereafter forming a metallic layer on aninsulating film on the surface of said semiconductor substrate aftersaid characteristics modifying step, said characteristics modifying stepincluding the step of heating said semiconductor substrate at atemperature which said metallic layer could not withstand but which saidpolycrystalline silicon electrode is able to withstand.